welding geometric shape imperfections general review
TRANSCRIPT
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A general review of geometric shape imperfections - types and causes
Job Knowledge Part 1. Introduction
Inthejobknowledgeseriesweldingimperfectionssuchascracks,lackoffusion,penetrationandporosityhavebeendiscussed.Thisarticlelooksatthoseimperfectionsrelatedtopoorgeometricshapeandwillconcentrateonthefollowing:
Excessweldmetal
Undercut
Overlap
Linearmisalignment Incompletelyfilledgroove
Suchimperfectionsmightbeconsideredasanomaliesinthejointandtheywillalwaysbepresenttosomedegreesothatitbecomesnecessarytoseparatetheacceptablefromtheunacceptable.Thisisdonebyfollowingguidancegivenbytheapplicationstandard,whichwasthebasisforthecomponentdesign,and/orbydirection,assetoutinthejobcontract.Examplesofstandardsthatmightbereferredtoare:
PD5500Specificationforunfiredfusionweldedpressurevessels.
BSENISO5817Welding.Fusion-weldedjointsinsteel,nickel,titaniumandtheiralloys(beamweldingexcluded).Qualitylevelsforimperfections
AWSD1.1Structuralweldingcode-Steel
Excess weld metal
also called cap height, overfill or reinforcement)
Fig.1.Excessweldmetal
Thisisweldmetallyingoutsidetheplanejoiningtheweldtoes.Notethattheterm'reinforcement',althoughusedextensivelyintheASME/AWSspecificationsisavoidedinEuropeasitimpliesitaddsstrengthtotheweldedjoint,whichisrarelythecase.
Common causes
Thisimperfectionisformedwhenexcessiveweldmetalisaddedtothejoint,whichisusuallyaresultofpoorweldertechniqueformanualprocessesbutmaybeduetopoorparameterselectionwhentheprocessismechanised.Thatis,toomuchfillermetalforthetravelspeedused.Inmulti-runweldingapoorselectionofindividualbeadsizescanresultinabeadbuild-uppatternthatoverfillsthejoint.Differentprocessesandparameters( egvoltage)canresultindifferentexcessweldmetalshapes.
Acceptance
Theacceptabilityofthisimperfectionisverydependentontheapplicationinwhichtheproductwillbeused.Moststandardshavelimit,relatedtomaterialthickness(eg10%),butalsohaveamaximumupperlimits.Boththeratioandthemaximummayberelatedtotheseverityofservicethatthecomponentisexpectedtosee.ThefollowingtablegivesexamplestakenfromBSENISO5817.
Excess weld metal limits for quality levels:
Severityofservice Moderate,D Stringent,B
Limit(uptomaximum) h=1mm+0.25b h=1mm+0.1b
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Maximum 10mm 5mm
Transitionrequired Smooth smooth
Where:h=heightofexcess&b=widthofbead(see figure1)
Animportantreasonforlimitingtheheightofexcessweldmetalisthatitrepresentsanon-valueaddedcost.However,itmustberememberedthattheheightoftheweldcapinfluencestheresultanttoeblend.Asharptransitioncausesalocalstressconcentrationthatcancontributetolossofstrength,whichisparticularlyimportantinfatiguesituations.Asaresultmostspecificationsstatethat'smoothtransitionisrequired'.
Avoidance
Iftheimperfectionisaresultofweldertechniquethenwelderretrainingisrequired.Formechanisedtechniquesanincreaseintravelspeedorvoltagewillhelptoreducecapheight.
Undercut
Fig.2.Undercut
Thisisanirregulargrooveatthetoeofarunintheparentmetal.Thefigureshowsundercutatsurfaceofacompletedjointbutitmayalsobefoundatthetoesofeachpassofamulti-runweld.Thelattercanresultinslagbecomingtrappedintheundercutregion.
Common causes
Whenarcandgaswelding,undercutisprobablythemostcommonshapeimperfection.Withsingle-sidedpipeweldsitmayalsobefoundattheboresurface.Itmayalsobeseenontheverticalfaceoffilletweldsmadeinthehorizontalverticalposition.Awidespreadingarc(higharcvoltage)withinsufficientfill(lowcurrentorhightravelspeed)istheusualcause.However,weldertechnique,especiallywhenweaving,andthewaytheweldingtorchisangledcanbothcauseandbeusedtoovercomeundercutting(ieangledtopushtheweldmetaltofillthemeltedgroove).Highweldingcurrentwillalsocauseundercut-thisisgenerallyassociatedwiththeneedforahightravelspeedtoavoidoverfillingofthejoint.
Acceptance
Largelybecausethisimperfectioniswidespread,moststandardspermitsomelevelofundercutalthoughtheydorequirethata'smoothtransitionisrequired.ThelimitsinBSENISO5817rangefrom0.5mm(stringent)to1mm(moderate)forthickness(t)greaterthan3mm(morestringentlimitsarerequiredfort0.5to3mm),whileAWSD1.1hasalimitof1mm.Measuringundercutcanbeaproblembecauseofthesmallsizeoftheimperfectioncomparedwiththegeneralenvironmentwheretherecanbemillscale,irregularitiesinthesurfaceandspatter.
Incriticalapplicationstheimperfectioncanbe'corrected'byblendgrindingorbydepositinganadditionalweldbead.
Avoidance
Thisimperfectionmaybeavoidedbyreducingtravelspeedand/ortheweldingcurrentandbymaintainingthecorrectarclength.
Overlap cold lapping)
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Fig.3.Overlap
Thisisanimperfectionatatoeorrootofaweldcausedbymetalflowingontothesurfaceoftheparentmetalwithoutfusingtoit.Itmayoccurinbothfilletandbuttwelds.
Common causes
Thisisoftencausedbypoormanipulationoftheelectrodeorweldinggun,especiallywhentheweldpoolislargeand'cold',wherethewelderallowsgravitytoinfluencetheweldshapebeforesolidification.Tightlyadherentoxidesorscaleonthemetalsurfacecanalsopreventtheweldmetalfusingwiththeparentmetaltocausetheoverlapimperfection.
Avoidance
Avoidanceisachievedthroughanacceptablelevelofwelderskillandareductioninweldpoolsize(obtainedbyreducingcurrentorincreasingtravelspeed).Adequatecleaningoftheparentplateisalsoimportant.
Acceptance
Standardsrarelyallowthepresenceofthisimperfection,unlessthelengthisshort( egBSENISO5817formoderatequalitylevelD).Overlapcanbeverydifficulttodetect,especiallyifitisextremelysmall.
Linear misalignment
Fig.4Linearmisalignment
(AlsoknownintheUSAashigh-low).Thisimperfectionrelatestodeviationsfromthecorrectposition/alignmentofthejoint.
Common causes
Thisisprimarilyaresultofpoorcomponentfit-upbeforewelding,whichcanbecompoundedbyvariationsintheshapeandthicknessofcomponents(egoutofroundnessofpipe).Tacksthatbreakduringweldingmayallowthecomponentstomoverelativetooneanother,againresultinginmisalignment.
Acceptance
Theacceptabilityofthisdefectisrelatedtothedesignfunctionofthestructureorpipelineeitherintermsoftheabilitytotakeloadacrossthemisalignmentorbecausesuchastepimpedestheflowoffluid.Acceptancevarieswiththeapplication:BSENISO5817relatesmisalignmenttowallthicknessbutsetsmaximumlimits( egformaterialthicknesst>3mmandmoderatelimitsofimperfectionsD,=0.25xt,withamaximumof5mm).
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AWSD1.1allows10%ofthewallthicknessuptoamaximumof3mm.Theconsequenceoflinearmisalignmentcan,whenweldingiscarriedoutfromoneside,belackofrootorsidewallfusiontogiveasharpcontinuousimperfectionalongthehigherweldfacetoe.Insomesituationslinearmisalignmentintheboreofapipecanleadtoin-serviceproblemswhereturbulenceofthecarrierfluidinthepipecreatessubsequenterosion.
Incomplete filled groove
Incompletefilledgroove
Thisisacontinuous,orintermittent,channelinthesurfaceofaweld,runningalongitslength,duetoinsufficientweldmetal.
Common causes
Thisproblemariseswhentherehasbeeninsufficientfillermetal(currentorwirefeedtoolowortoohighatravelspeed)sothatthejointhasnotbeensufficientlyfilled.Theresultisthatthethicknessofweldmentislessthanthatspecifiedinthedesign,whichcouldleadtofailure.
Acceptance
Moststandardswillnotacceptthistypeofimperfection,exceptperhapsovershortlengthsandeventhenasmoothtransitionisrequired.Thedesignerexpectsthejointtobeadequatelyfilled,butnottoomuchso(seeexcessweldmetal).Oftenthepresenceofthisimperfectionisanindicationofpoorworkmanshipandcouldsuggestthatfurthertrainingisrequired.
Continuation
Part2looksatshapeimperfectionssuchasexcesspenetrationandrootconcavityandhighlightsshapeimperfectionsrelatedtofilletweldedjoints.
Thissecondarticleonshapeimperfectionsrefersmostlytofilletweldsbuttherearetwoadditionalbuttweldimperfectionsthatrequiresomecomment.Excessive penetration Excess penetration bead)
Fig.1.ExcesspenetrationExcessweldmetalprotrudingthroughtherootofafusion(butt)weldmadefromonesideonly.Withpipeweldingthistypeofimperfectionmaycauseeffectsinthefluidflowthatcancauseerosionand/orcorrosionproblems.Common causes
Penetrationbecomesexcessivewhenthejointgapistoolarge,therootfacesaretoosmall,theheatinputtothejointistoohighoracombinationofthesecauses.
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Acceptance
Thecriteriawhichsetsthelevelofacceptablepenetrationdependsprimarilyontheapplicationcodeorspecification.BS2971(Class2arcwelding)requiresthatthe'penetrationbeadshallnotexceed3mmforpipesuptoandincluding150mmboreor6mmforpipesover150mmbore'.BS2633(Class1arcwelding)givesspecificlimitsforsmallerdiameterspipes,egforpipesize25-50mmthemaximumallowedborepenetrationis2.5mm.ASMEB31.3basesacceptabilityonthenominalthicknessoftheweld,forinstance,allowingforathicknessrangeof13-25mmupto4mmofprotrusion.However,ASMEnotesthat'morestringentcriteriamaybespecifiedintheengineeringdesign'.BSENISO5817(Qualitylevelsforimperfections),whichsupersedesBSEN25817,relatestheacceptableprotrusionto
thewidthoftheunder-beadasfollows:
Severity of service Moderate, D Stringent, B
Limit(uptomaximum) h1mm+1.0b h1mm+0.2b
Maximum 5mm 3mm
Forthicknesses>3mmwhere:h=heightofexcess&b=widthofroot (seeFig.1)
Avoidance
Itisimportanttoensurethatjointfit-upisasspecifiedintheweldingprocedure.Ifweldertechniqueistheproblemthenretrainingisrequired.Root concavity suck-back; underwashing)
Fig.2.RootconcavityAshallowgroovethatmayoccurintherootofabuttweld.Common causes
Rootconcavityiscausedbyshrinkageoftheweldpoolinthethrough-thicknessdirectionoftheweld.Meltingoftherootpassbythesecondpasscanalsoproducerootconcavity.ThisimperfectionisfrequentlyassociatedwithTIGweldingwiththemostcommoncausebeingpoorpreparationleavingtherootgapeithertoosmallor,insomecases,toolarge.Excessivelyhighweldingspeedsmaketheformationofrootconcavitymorelikely.Acceptance
Therootconcavitymaybeacceptable.Thiswilldependontherelevantstandardbeingworkedto.Forexample:BS2971requiresthat:a)thereiscompleterootfusionb)thethicknessoftheweldisnotlessthanthepipethickness.ASMEB31.3requiresthatthe'totaljointthickness,includingweldreinforcement,mustbegreaterthantheweldthickness'BSENISO5817setsupperlimitsrelatedtothequalitylevel,egforthicknesses>3mmModerate,(D),h0.2tbutmax2mmforStringent,(B),h0.05tbutmax0.5mm.Furthermore,asmoothtransitionisrequiredattheweldtoes. Ineffectthestandardsrequirethattheminimumdesignthroatthicknessofthefinishedweldmentisachieved.Ifthefirsttwoconditionsofacceptancearemetbuttheweldfacedoesnothaveasufficientlyhighcap,additionalweldmetalmaybedepositedtoincreasethethroat.Avoidance
Itisimportanttoensurethatjointfit-upisasspecifiedintheweldingprocedureandthatthedefinedparametersarebeingfollowed.Ifweldertechniqueistheproblemthenretrainingisrequired.Fillet welded joints
ThisSectionshouldbereadinconjunctionwithJobKnowledge66Filletweldedjoints-areviewofthepracticalities. Excessive convexity
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Fig.3.ExcessiveconvexityThisfeatureisalsocoveredbythedefinitionforexcessweldmetal,seePart1,andmaybedescribedasweldmetallyingoutsidetheplanejoiningtheweldtoes.Notethattheterm'reinforcement',althoughusedextensivelyintheASME/AWSspecificationsisavoidedinEuropeasitimpliesthatexcessmetalcontributestothestrengthoftheweldedjoint.Thisisrarelythecase.Common causes
Poortechniqueandthedepositionoflargevolumesof'cold'weldmetal.Acceptance
Theidealiseddesignrequirementofa'mitre'filletweldisoftendifficulttoachieve,particularlywithmanualweldingprocesses.
BSENISO5817acceptanceisbasedonamitrefilletweldshapewithaspecificdesignthroatandanyexcessweldmetalismeasuredinrelationtothismitresurface.Thelimitsforthisimperfectionrelatetheheightoftheexcessmetaltothewidthofthebeadwithmaximumvaluesrangingfrom3mmforastringentqualitylevelto5mmforamoderatequalitylevel.Surprisingly,thereisnoreferencetoa'smoothtransition'beingrequiredattheweldtoesforsuchweldshape.AWSD1.1alsohaslimitsrelatingwidthtoacceptableexcessasfollows:
Width of weld face Maximum convexity
W8mm 2mm
W
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Undersized fillet welds fillet welds smaller than those specified)
Fig.5.UndersizedfilletweldCommon causes
Theweldingrelatedcausesareassociatedwithhighweldingspeedsandlowweldingcurrents.Acceptance
Therefore,itisnormallyassumedthatfilletweldswillbeatleastofthesizespecified.BSENSIO5817statesthatlimitstoinsufficientthroatthicknessarenotapplicabletoprocesseswithproofofgreaterdepthofpenetration,thereforeafilletweldwithanapparentthroatthicknesssmallerthatthatprescribedshouldnotberegardedasbeingimperfectiftheactualthroatthicknesswithacompensatinggreaterdepthofpenetrationcomplieswiththenominalvalue.Thatisifwecanbe
surethereisgoodpenetrationthesmallerfilletmaybeacceptable,however,thisshouldbediscussedwiththedesignerofthefabrication.Thelimitssetbythestandard.Relyingupondeeppenetrationtoprovidetherequiredminimumdesignthroatthicknesscanbedifficulttojustify.Penetrationisaweldcharacteristicthatishardtomeasuredirectlyandreliancemustbeplacedonthestringentcontrolofboththeweldingprocessandthewelder.Manualweldingcanrarelybereliedupontoprovidetherequiredconsistencybutitisanoptionwithmechanisedweldingsystems.
Imperfection: fillet weld
having a throat
thickness smaller than
the nominal value
Quality levels
ModerateD IntermediateC StringentB
LongimperfectionsNOTpermitted NOTpermitted
Shortimperfections(seeFig.5)h0.3mm+0.1a
max2mm max1mm
Avoidance
Adheretothespecifiedweldingprocedureandparameters.Usesufficientcurrentandappropriatetravelspeed.Wherepossiblemechanisetheweldingoperation.Asymmetric fillet weld a fillet weld where the legs are of unequal length)
Fig.6.AsymmetricfilletweldCommon causes
Duetoincorrectelectrodepositioningortogravitypullingthemoltenpooltowardsonefaceofthejoint.Itisanmainlyaproblemwithfilletweldsmadeinthehorizontal/vertical(PB)position.Acceptance
Thereareinstanceswhereasymmetrymaybespecified(egtoplacethetoestressconcentrationinaparticularregion).BSENISO5817would,fora10mmleglengthfilletweld( ie7.1mmthroat)allowadifferenceinleglengthsofabout2.5mmatthestringentqualityleveland3.4mmatthemoderatequalitylevel.Acceptanceisrelatedtothethroatthickness.
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Theconsequenceofthisimperfectionisasignificantincreaseinweldvolume.Providedtheleglengthrequirementisachievedtherewouldnotbealossofstrength.Perhapsthisiswhy,inotherstandards,arequirementisnotspecifiedandtheacceptabilityislefttotheinspectionpersonneltomakethe'engineeringjudgement'!Poor fit-up
Fig.7.Poorfit-upThemostcommonimperfectionisanexcessivegapbetweenthematingfacesofthematerials.Common causes
Poorworkshoppractice,poordimensioningandtolerancedimensionsondrawings.
AcceptanceAmajorproblemwithfilletweldsisensuringthegapbetweenthecomponentsiswithindefinedlimits.BSENISO5817specifiestheacceptancecriteriaasfollows:
Qualitylevels
ModerateD IntermediateC StringentB
h1mm+0.3ah0.5mm+0.2ah0.5mm+0.1a
max4mm max3mm max2mm
Whereh=fit-upgapanda=filletwelddesignthroat
Figure7showsthatthegapresultsinareductionintheleglengthontheverticalplateandthis,inturn,resultsinareductioninthethroatthicknessofthejoint.A10mmleglengthfilletwitharootgapof3mmgivesaneffectivelegof7mm(athroatof4.9mminsteadoftheexpected7mm).WhentheapplicationofBSENISO5817isnotrequired,theguidanceofBSEN1011-2canbefollowed,which
recommendsamaximumgapof3mm.Thisstandardalsostatesthatthesizeofthefilletweldcanbeincreasedtocompensateforalargegap.ThisdiscrepancyisaddressedwithinAWSD1.1.whichpermitsarootgapofupto5mmformaterialthicknessupto75mm.However,'ifthe(joint)separationisgreaterthan2mmthelegofthefilletweldshallbeincreasedbytheamountoftherootopening,orthecontractorshalldemonstratethattheeffectivethroathasbeenobtained'.
Fillet welded joints - a review of the practicalities
Job Knowledge
Filletweldedjointssuchastee,lapandcornerjointsarethemostcommonconnectioninweldedfabrication.Intotaltheyprobablyaccountforaround80%ofalljointsmadebyarcwelding.Itislikelythatahighpercentageofotherjoiningtechniquesalsousesomeformofafilletweldedjointincludingnon-fusionprocessessuchasbrazing,brazeweldingandsoldering.Thelattertechniquesareoutsidethescopeofthisarticle.
Althoughthefilletweldissocommon,thereareanumberofaspectstobeconsideredbeforeproducingsuchaweld.Thisarticlewillreviewanumberoftopicsthatrelatetofilletweldedjointsanditishopedthateventhemostseasonedfabricatororweldingpersonwillgainfromthisarticleinsomeway.CommonjointdesignsforfilletweldsareshownbelowinFig.1.
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Fig1.Commonjointdesignsforfilletwelds
Fillet weld features
ISO2553(EN22553)usesthefollowingnotationasFigs.2and3show.a=throatthicknessz=leglengths=deeppenetrationthroatthicknessl=lengthofintermittentfillet
Fig.2.Mitrefillet
Fig3.Deeppenetrationfillet
Fillet weld shapes
Over specified fillet welds or oversized fillet welds
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Fig4.Weldsizesinrelationtotherequiredleglengthsorthroatthickness
Oneofthegreatestproblemsassociatedwithfilletweldedjointsisachievingthecorrectweldsizeinrelationtotherequiredleglengthsorthroatthickness(Fig.4).Thedesignermaycalculatethesizeandallowa'safetyfactor'sothattheweldspecifiedonthefabricationdrawingislargerthanisrequiredbydesignconsiderations.Theweldsizeiscommunicatedbyusinganappropriateweldsymbol.IntheUKtheweldsizeisfrequentlyspecifiedbyreferringtotheleglength'z'inISO2553wherethenumbergivestheweldsizeinmillimetresasshowninFig.5.
Fig5.Weldsizespecification(UK)
InEurope,itismorecommontofindthedesignthroatthickness,'a'specified( Fig.6).
Fig6.Weldsizespecification(Europe)
Oncethedrawinghasbeenissuedtotheshopfloor,itisusualtofindanadditionalsafetyfactoralsobeingappliedonbythewelderorinspector.Itisalsocommontohear'addabitmoreitwillmakeitstronger'.Theoutcomeisanoversizedweldwithperhapsan8mmleglengthratherthanthe6mmspecifiedbythedesigner.Thisextra2mmconstitutesanincreaseinweldvolumeofover80%.Thiscoupledwiththealreadyoverspecifiedweldsizefromthedesigner's'safetyfactor'mayleadtoaweldthatistwicethevolumeofacorrectlysizedfilletweld.Bykeepingtheweldtothesizespecifiedbythedrawingoffice,fasterweldingspeedscanbeachieved,thereforeincreasingproductivity,reducingoverallproductweight,consumableconsumptionandconsumablecost.
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Theotherbenefitisthat,inthecaseofmostarcweldingprocesses,aslightincreaseintravelspeedwouldinmostcasesseeanincreaseinrootpenetrationsothattheactualthroatthicknessisincreased:Anoversizedweldisthereforeverycostlytoproduce,maynothave'betterstrength'andiswastefulofweldingconsumablesandmayseeotherfabricationproblemsincludingexcessivedistortion.
Lap joints welded with fillet welds.
Asdiscussedearlier,oversizedweldsarecommonplaceandthelapjointisnoexception.ThedesignermayspecifyaleglengththatisequaltothematerialthicknessasinFig.7.
Fig7.Lapjoint-leglengthspecification
Strengthconsiderationsmaymeanthatthefilletweldsizeneednotbeanywhereneartheplatethickness.Inpracticetheweldmayalsobedeficientinotherwaysforexample:
Fig8.Exampleshowinganundersizedfilletweld
Duetomeltingawayofthecorneroftheupperplate(Fig.8),theverticalleglengthisreducedmeaningthatthedesignthroathasalsobeenreduced;thereforeanundersizedweldhasbeencreated.Careisthereforeneededtoensurethatthe
corneroftheupperplateisnotmeltedaway.Ideallytheweldshouldbesome0.5-1mmclearofthetopcorner( Fig.9).
Fig9.Ideallytheweldshouldbe0.5-1mmclearofthetopcorner
Itmaybethedesignermaythereforespecifyaslightlysmallerleglengthcomparedtothethicknessofthecomponent.Tocompensateforthisreductioninthroatthicknessitmaybenecessarytospecifyadeeppenetrationfilletweld.Thisamountofadditionalpenetrationwouldneedtobeconfirmedbysuitableweldtests.Additionalcontrolsmayalsobeneededduringproductionweldingtoensurethatthisadditionalpenetrationisbeingachievedconsistently.Inadditiontothereductioninthroatthicknessthereisthepotentialforadditionalproblemssuchasoverlapattheweldtoeduetothelargerweldpoolsize(Fig.10)oranexcessivelyconvexweldfaceandconsequentialsharpnotchesattheweldtoe(Fig.11).
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Fig10.Overlapattheweldtoeduetothelargerweldpoolsize
Fig11.Excessivelyconvexweldfaceandconsequentialsharpnotchesattheweldtoe
BoththepotentialproblemsshowninFigs.10and11couldadverselyinfluencethefatiguelifeoftheweldedjointduetotheincreasedtoeangle,whichactsasagreaterstressconcentration.Poorfit-upcanalsoreducethethroatthicknessasinFig.12.Thecorneroftheverticalcomponenthasbeenbevelledinthesketchinanexaggeratedmannertoillustratethepoint.
Fig12.Throatthicknessmaybereducedbypoorfit-up
Summary
Filletweldedjointsarenotonlythemostfrequentlyusedweldjointsbutarealsooneofthemostdifficulttoweldwithanyrealdegreeofconsistency.Filletweldsrequireahigherheatinputthanabuttjointofthesamethicknessand,withlessskilledweldersthiscanleadtolackofpenetrationand/orfusiondefectsthatcannotbedetectedbyvisualexaminationandotherNDTtechniques.FilletweldedjointsarenotalwaysopentoNDTorareindeedtimeconsumingtomanynon-destructivelytestingtechniquessuchasradiographyorultrasonictestingandtheresultsareoftendifficulttointerpret.Inspectionmethodssuchasvisualinspection,magneticparticleinspectionandpenetrantinspectionaresurfaceexaminationtechniquesonlyandwithvisualinspection,muchoftheeffortisexpendedinmeasuringthesizeoftheweldratherthanidentifyingother
qualityaspects.Filletweldedjointsarethereforemuchmoredifficulttoweldandinspect.Oftentheweldsthatareproducedarelargerthantheyneedtobeortheymaybeofapoorshapewhichcanadverselyinfluencetheirserviceperformance.Toovercomethesedifficulties,designersneedtospecifyaccuratelythemostappropriatethroatsizeandweldingpersonnelshouldstrivetoachievethespecifieddesignsize.Weldersalsoneedtobeadequatelytrainedandsufficientlyskilledtobecapableofmaintaininganacceptableweldquality.ThisarticlewaswrittenbyMark Cozens of Weld-Class Solutions.AnyenquiriesregardingthecontentofthearticleshouldbeaddressedinitiallytotheEditor,Connect.
A review of the application of weld symbols on drawings - Part 2
Job Knowledge
Part1ofthisarticlewhichappearedintheMay/JuneissueofConnect,dealtwiththemostbasicweldsymbolsasthey
appearonengineeringdrawings.Aspreviouslymentioned,itisessentialthatallconcernedinanyprojectareawareofwhichStandardisbeingapplied.
Weld sizing
Inorderthatthecorrectsizeofweldcanbeapplied,itiscommontofindnumberstoeithertheleftortotherightofthesymbol.Forfilletwelds,numberstotheleftofthesymbolindicatethedesignthroatthickness,leglength,orbothdesignthroatthicknessandleglengthrequirements.Figure1givesexamplesofsymbolsusedindifferentStandards.
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Fig.1
Forfilletwelds:SupersededBS499Pt2gives
a=designthroatthicknessb=leglength
ISO2553/EN22553requirements
a=designthroatthicknessz=leglength
s=penetrationthroatthickness
Forbuttjointsandwelds,anSwithanumbertotheleftofasymbolreferstothedepthofpenetrationasshownin Fig.2.
Fig.2
Whentherearenospecificdimensionalrequirementsspecifiedforbuttweldsonadrawingusingweldsymbols,itwouldnormallybeassumedthattherequirementisforafullpenetrationbuttweld( Fig.3).
Fig.3
Numberstotherightofasymbolorsymbolsrelatetothelongitudinaldimensionofwelds, egforfillets,thenumberofwelds,weldlengthandweldspacingfornon-continuouswelds,asFig.4.
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Fig.4
Onfilletweldedjointsmadefrombothsides,astaggeredweldcanbeshownbyplacinga'Z'throughthereferenceline(Fig.5).
Fig.5
Supplementary symbols
Weldsymbolsindicatethetypeofpreparationtouseortheweldtype.However,theremaystillbeoccasionswhereotherinformationisrequired.ThebasicinformationcanthereforebeaddedtoinordertoprovidefurtherdetailsasshowninFigs.6,7and8.
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Fig.6
Fig.7
Fig.8
Weld all round
ForaRectangularHollowSection(RHS)weldedtoaplate,forexample:
Weld in the field or on site
Theboxattachedtothearrowcanbeusedtocontain,orpointto,otherinformation.
Welding process type
ISO4063givesweldingprocessesspecificreferencenumbers.AsshowninFig.9theappropriateprocessnumberisplacedinthetailofthearrow.Otherprocessesaregivenauniquenumber.Inthisexample,135referstoMAGwelding.
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Fig.9
ThereareanumberofadditionalsymbolsgivenintheStandards(egISO22553)whichrefertoadditionalweldingorjointrequirements.Figure10showstherequirementforasealingrun.
Fig.10
Compound joints/welds
Acompoundweldcouldbea'T'buttweldwhichrequiresfilletweldstobeaddedtoincreasethethroatthicknessasshowninFig.11.
Fig.11
The broken reference line
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Fig.12
ThemainfeaturethatdistinguishesweldsymbolstandardsisthatforISO2553andBSEN22553,thereisanadditionalfeatureofabrokenreferenceline.Thismethodisusedwhenaweldmentorweldpreparationneedstobespecifiedonthe'otherside'ofthearrowasshowninFig.12.
Anysymbolthatisusedtoshowajointorweldtypefeatureontheothersideofthearrowlineisalwaysplacedonadottedline.BS499andAWSrequiresymbolstobeplacedabovethereferenceline(whichindicatetheotherside)orbelowthereferenceline(indicatingthearrowside).
Summary
Weldsymbolsareaveryusefulwayofcommunicatingweldingrequirementsfromthedesignofficetotheshopfloor.Itisessentialthatthe'rules'ofthestandardusedarecorrectlyappliedbydrawingofficepersonnel.However,itisalsoimportantthatshopfloorpersonnelareabletoreadandunderstandthedetailsofweldsymbols.Muchofthisrequirementcanbemetbyreferencetothestandardbeingusedwithintheorganisationandbythedrawingofficepersonnelconsideringtheneedsoftheendusersuchasthewelders,weldingsupervisors,weldinginspectionpersonnelandweldingengineersinordertominimisecostlymistakesduetomisinterpretation.
Trainingofallpersonnelinthecorrectuseofweldsymbolspecificationsalsoplaysanimportantroleinensuringthatweldsymbolsarebothcorrectlyappliedandcorrectlyread.ThisarticlewaswrittenbyMark CozensofWeld-Class Solutions.